Nylons are polyamides which are generally synthesized by the condensation polymerization of a diamine with a dicarboxylic acid. Similarly, Nylons may be produced by the condensation polymerization of lactams. A ubiquitous nylon is Nylon 6,6, which is produced by condensation polymerization of hexamethylenediamine (HMD) and adipic acid. Nylon 6 can be produced by a ring opening polymerization of caprolactam (Anton & Baird, Polyamides Fibers, Encyclopedia of Polymer Science and Technology, 2001).
Nylon 5, Nylon 5,5 and other variants including C5 monomers represent novel polyamides with value-added characteristics compared to Nylon 6 and Nylon 6,6 in a number of applications. Nylon 5 is produced by polymerisation of 5-aminopentanoic acid, whereas Nylon 5,5 is produced by condensation polymerisation of glutaric acid and cadaverine. No economically viable petrochemical routes exist to producing the monomers for Nylon 5 and Nylon 5,5.
Given no economically viable petrochemical monomer feedstocks, biotechnology offers an alternative approach via biocatalysis. Biocatalysis is the use of biological catalysts, such as enzymes, to perform biochemical transformations of organic compounds.
Both bioderived feedstocks and petrochemical feedstocks are viable starting materials for the biocatalysis processes.
Accordingly, against this background, it is clear that there is a need for sustainable methods for producing one or more of glutaric acid, 5-hydroxypentanoate, 5-aminopentanoate, cadaverine and 1,5-pentanediol (hereafter “C5 building blocks”) wherein the methods are biocatalyst based.
However, wild-type prokaryotes or eukaryotes do not overproduce such C5 building blocks to the extracellular environment. Nevertheless, the metabolism of glutaric acid, 5-aminopentanoate and cadaverine has been reported.
The dicarboxylic acid glutaric acid is converted efficiently as a carbon source by a number of bacteria and yeasts via β-oxidation into central metabolites. Decarboxylation of Coenzyme A (CoA) activated glutarate to crotonyl-CoA facilitates further catabolism via β-oxidation.
The metabolism of 5-aminopentanoate has been reported for anaerobic bacteria such as Clostridium viride (Buckel et al., 2004, Arch. Microbiol., 162, 387-394). Similarly, cadaverine may be degraded to acetate and butyrate (Roeder and Schink, 2009, Appl. Environ. Microbiol., 75(14), 4821-4828)
The optimality principle states that microorganisms regulate their biochemical networks to support maximum biomass growth. Beyond the need for expressing heterologous pathways in a host organism, directing carbon flux towards C5 building blocks that serve as carbon sources rather than as biomass growth constituents, contradicts the optimality principle. For example, transferring the 1-butanol pathway from Clostridium species into other production strains has often fallen short by an order of magnitude compared to the production performance of native producers (Shen et al., Appl. Environ. Microbiol., 2011, 77(9):2905-2915).
The efficient synthesis of the five carbon aliphatic backbone precursor is a key consideration in synthesizing one or more C5 building blocks prior to forming terminal functional groups, such as carboxyl, amine or hydroxyl groups, on the C5 aliphatic backbone.